U.S. patent application number 13/564338 was filed with the patent office on 2013-02-07 for systems and methods for drilling boreholes with noncircular or variable cross-sections.
This patent application is currently assigned to Halliburton Energy Services, Inc.. The applicant listed for this patent is Blaine C. COMEAUX, Ronald J. Dirksen. Invention is credited to Blaine C. COMEAUX, Ronald J. Dirksen.
Application Number | 20130032406 13/564338 |
Document ID | / |
Family ID | 47002551 |
Filed Date | 2013-02-07 |
United States Patent
Application |
20130032406 |
Kind Code |
A1 |
COMEAUX; Blaine C. ; et
al. |
February 7, 2013 |
Systems and Methods for Drilling Boreholes with Noncircular or
Variable Cross-Sections
Abstract
In a pulsed-electric drilling system, a nonrotating bit is given
a noncircular shape to drill a correspondingly-shaped borehole,
e.g., triangular, rectangular, polygonal, oval, or a more complex
shape. Some embodiments employ a reconfigurable bit that deploys
extensions as needed to dynamically vary the cross-section of the
borehole at selected locations. In this fashion, a driller is able
to create borehole with a preferred cross-sectional shape to, e.g.,
drill the smallest possible hole while simultaneously providing
additional clearance for equipment or instrumentation, additional
surface area for well inflow, channels for improved borehole
cleaning, teeth for improved cementing, reduced contact area to
reduce drag on the drillstring, or any other benefits achievable by
customizing the borehole cross-section.
Inventors: |
COMEAUX; Blaine C.; (Spring,
TX) ; Dirksen; Ronald J.; (Spring, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
COMEAUX; Blaine C.
Dirksen; Ronald J. |
Spring
Spring |
TX
TX |
US
US |
|
|
Assignee: |
Halliburton Energy Services,
Inc.
Houston
TX
|
Family ID: |
47002551 |
Appl. No.: |
13/564338 |
Filed: |
August 1, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61514333 |
Aug 2, 2011 |
|
|
|
Current U.S.
Class: |
175/57 ;
175/416 |
Current CPC
Class: |
E21C 37/18 20130101;
E21B 10/5673 20130101; E21B 10/32 20130101; E21B 7/15 20130101;
E21B 7/001 20130101 |
Class at
Publication: |
175/57 ;
175/416 |
International
Class: |
E21B 10/36 20060101
E21B010/36; E21B 7/00 20060101 E21B007/00 |
Claims
1. A method for drilling a noncircular borehole, the method
comprising: maintaining a bit in position at a bottom of a borehole
without rotating said bit through more than 60.degree. per inch of
forward progress, said bit having a noncircular transverse
cross-section; detaching material from the bottom of the borehole
with pulses of electrical current; and flushing detached material
from the borehole with a flow of drilling fluid.
2. The method of claim 1, wherein said maintaining includes: adding
lengths of tubing to a drillstring to which the bit is mounted;
extending the drillstring into the borehole; and rotating the
drillstring during said extending.
3. The method of claim 1, wherein the bit is not rotated more than
15.degree. per inch of forward progress.
4. The method of claim 1, wherein the bit is not rotated more than
3.degree. per inch of forward progress.
5. The method of claim 1, wherein the bit is not systematically
rotated.
6. The method of claim 1, wherein the noncircular transverse
cross-section is a regular polygon having no more than six
sides.
7. The method of claim 1, wherein the noncircular transverse
cross-section is finned or star-shaped.
8. The method of claim 1, wherein the noncircular transverse
cross-section is elliptical.
9. The method of claim 1, further comprising: varying the
transverse cross-section of the bit at different positions in the
borehole.
10. The method of claim 1, further comprising cutting a downhole
core sample with a square cross-section.
11. A system for drilling a noncircular borehole, the system
comprising: a bit that extends a borehole without rotating through
more than 60.degree. per inch by detaching formation material with
pulses of electric current, said bit having a noncircular
transverse cross-section; and a drillstring that defines at least
one path for a fluid flow to the bit to flush detached formation
material from the borehole.
12. The system of claim 11, wherein the drillstring attaches to the
bit by a swivel or other mechanism that enables the drillstring to
rotate at a higher rate than the bit.
13. The system of claim 11, wherein the bit is substantially
non-rotating.
14. The system of claim 11, wherein the noncircular transverse
cross-section is a regular polygon having no more than six
sides.
15. The system of claim 11, wherein the noncircular transverse
cross-section is finned or star-shaped.
16. The system of claim 11, wherein the noncircular transverse
cross-section is elliptical.
17. The system of claim 11, wherein the bit has extensions that
enable the transverse cross-section to be varied at different
borehole positions.
18. The system of claim 11, wherein the bit is configured to cut a
downhole core sample with a square cross-section.
Description
RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Application
61/514,333, titled "Systems and methods for drilling boreholes with
noncircular or variable cross-sections" and filed Aug. 2, 2011 by
Blaine Comeaux and Ron Dirksen. The foregoing application is hereby
incorporated herein by reference.
BACKGROUND
[0002] There have been recent efforts to develop drilling
techniques that do not require physically cutting and scraping away
material to form the borehole. Particularly relevant to the present
disclosure are pulsed electric drilling systems that employ high
energy sparks to pulverize the formation material and thereby
enable it to be cleared from the path of the drilling assembly.
Illustrative examples of such systems are disclosed in: U.S. Pat.
No. 4,741,405, titled "Focused Shock Spark Discharge Drill Using
Multiple Electrodes" by Moeny and Small; WO 2008/003092, titled
"Portable and directional electrocrushing bit" by Moeny; and WO
2010/027866, titled "Pulsed electric rock drilling apparatus with
non-rotating bit and directional control" by Moeny. Each of these
references is incorporated herein by reference.
[0003] Generally speaking, the disclosed drilling systems employ a
bit having multiple electrodes immersed in a highly resistive
drilling fluid at the bottom of a borehole. The systems generate
multiple sparks per second using a specified excitation current
profile that causes a transient spark to form and arc through the
most conducting portion of the borehole floor. The arc causes that
portion of the borehole floor to disintegrate or fragment and be
swept away by the flow of drilling fluid. As the most conductive
portions of the borehole floor are removed, subsequent sparks
naturally seek the next most conductive portion.
[0004] To date all oilfield drilling systems known to the authors
create circular boreholes. While satisfactory for many purposes,
there are situations in which this limitation creates
inefficiencies in the drilling process, e.g., by requiring a much
larger volume of material to be removed from the borehole than is
truly necessary.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] Accordingly, there are disclosed herein in the drawings and
detailed description specific embodiments of systems and methods
for drilling boreholes with noncircular or variable cross-sections.
In the drawings:
[0006] FIG. 1 shows an illustrative pulsed-electric drilling
environment.
[0007] FIG. 2 is a detail view of an illustrative drill bit.
[0008] FIG. 3 shows an illustrative coring bit having a square
cross-section.
[0009] FIG. 4 shows an illustrative drill bit having a finned
cross-section.
[0010] FIGS. 5A-5C show illustrative variable cross-section
boreholes.
[0011] FIGS. 5D-5G show illustrative boreholes with noncircular
cross-sections.
[0012] FIG. 6 is a function-block diagram of illustrative tool
electronics.
[0013] FIG. 7 is a flowchart of an illustrative drilling
method.
[0014] It should be understood, however, that the specific
embodiments given in the drawings and detailed description do not
limit the disclosure. On the contrary, they provide the foundation
for one of ordinary skill to discern the alternative forms,
equivalents, and modifications that are encompassed in the scope of
the appended claims.
DETAILED DESCRIPTION
[0015] Systems and methods for drilling boreholes with noncircular
cross-sections and/or variable cross-sections. The disclosed
systems employ a pulsed electric drilling system such as that
disclosed by Moeny in the above-identified references. Because such
systems do not require drill bit rotation, the bits can be given a
noncircular shape to drill boreholes with corresponding shapes,
e.g., triangular, rectangular, polygonal, oval, or more complex
shapes including crosses, star-shapes, and finned. (As used herein,
a fin is a relatively thin, flat projection from a central region.)
Further, the bits can be made configurable to extend electrodes or
deploy arms or other extensions to change the cross-section of the
borehole at selected locations.
[0016] In this fashion, a driller is able to create borehole in
subterraneous earth or at surface with a preferred cross-sectional
shape. The desire to create a specific shape of hole in a downhole
well can be driven by the need to locate special equipment that
does not conform to a circular hole shape or that would require an
excessively large circular hole to provide sufficient clearance
around the equipment. For example, devices for downhole remote
sensing, monitoring, and actuation (commonly referred to as
"Smartwell" technology) may be included in a casing string or
attached to the outside of the casing string, creating a "bulge" on
one edge of an otherwise circular cross-section. Such technology
may benefit from additional clearance along one side of casing to
accommodate the bulge. By limiting the amount of rock that must be
removed to only what is required, the drilling costs and time
should be reduced, as well as the amount of cuttings that must be
disposed off.
[0017] Other potential advantages to a noncircular hole shape
include: reduced wall contact with the drillstring (and hence less
friction), channels for more effective flushing of debris from the
borehole, increased effective permeability in production zones, and
improved cementing performance. These and other competitive
advantages may arise from having the flexibility to drill a shape
other than a circle for whatever purposes the user desires.
[0018] The disclosed embodiments can be best understood in the
context of their environment. Accordingly, FIG. 1 shows a drilling
platform 2 supports a derrick 4 having a traveling block 6 for
raising and lowering a drill string 8. A drill bit 26 is powered
via a wireline cable 30 to extend borehole 16. Power to the bit is
provided by a power generator and power conditioning and delivery
systems to convert the generated power into multi-kilovolt DC
pulsed power required for the system. This would likely be done in
several steps, with high voltage cabling being provided between the
different stages of the power-conditioning system. The power
circuits will generate heat and will likely be cooled during their
operation to sustain operation for extended periods.
[0019] Recirculation equipment 18 pumps drilling fluid from a
retention pit 20 through a feed pipe 22 to kelly 10, downhole
through the interior of drill string 8, through orifices in drill
bit 26, back to the surface via the annulus around drill string 8,
through a blowout preventer and along a return pipe 23 into the pit
20. The drilling fluid transports cuttings from the borehole into
the pit 20, cools the bit, and aids in maintaining the borehole
integrity. A telemetry interface 36 provides communication between
a surface control and monitoring system 50 and the electronics for
driving bit 26. A user can interact with the control and monitoring
system via a user interface having an input device 54 and an output
device 56. Software on computer readable storage media 52
configures the operation of the control and monitoring system.
[0020] FIG. 2 shows a close-up view of an illustrative formation 60
being penetrated by drill bit 26. Electrodes 62 on the face of the
bit provide electric discharges to form the borehole 16. A
high-permittivity, high-resistivity drilling fluid flows from the
bore of the drill string through one or more ports in the bit to
pass around the electrodes and return along the annular space
around the drillstring. The fluid serves to communicate the
electrical discharges to the formation and to cool the bit and
clear away the debris.
[0021] Though the bit is shown as having a circular transverse
cross-section in FIG. 2, this is not a requirement. Bits that are
noncircular and/or reconfigurable can be used as part of a system
designed to destroy rock by transmitting very high current into the
rock via electrodes mounted on the face of a drill bit structure.
The electric arcs propagate into the rock ahead of the electrode
and back to the grounding elements on the drill bit. The
arrangement of the electrodes and grounding elements in a given
pattern will determine the shape of the hole that is created.
[0022] For example, FIG. 3 shows a coring bit 26 having a square
(inner and outer) cross-section to cut a square borehole 16 while
simultaneously obtaining a square core 66. In addition to providing
cores that are easier to analyze, the illustrated configuration
enables the relative orientation between the core and the borehole
to be determined, maintained, and employed in later operations. For
example, the illustrated configuration offers an opportunity for
identifying rock grain orientations relative to the borehole and
employing that knowledge for increased completion effectiveness
using directional completion techniques (e.g., oriented projectiles
or oriented fracturing jets).
[0023] The coring bit 26 can be designed to periodically cut the
core for transport to the surface. In some embodiments, the cutting
is performed when the bit detects a change in rock morphology,
e.g., based on at-bit resistivity measurements. Many coring bits
exist and can be used as a guide for the implementation of a
noncircular pulsed-electric coring bit. This bit design can also be
employed for sidewall coring operations.
[0024] By mounting the electrodes and grounding elements on movable
components, the shape of the hole created can be changed
on-the-fly, i.e., without tripping out of the well. For example,
the downhole assembly may be equipped with a mechanism for
extending the electrodes laterally into the side wall, either a few
inches for collecting a core of the formations or for generating a
drainage hole of significant length (e.g., tens to thousands of
feet) into the formations at a desired depth. The mechanism for
extending the electrodes may also be utilized to enlarge the
borehole over a specific desirable interval or multiple intervals
or over the entire length of borehole drilled.
[0025] FIG. 4 shows an illustrative bit with extendable arms 72 to
cut slots along the borehole wall. The arms can be retracted for
regions of the borehole where slots are not desired. The electrodes
provide pulverization of the formation without requiring a
substantial force, thereby making it possible to provide
configurable drill bits without requiring an extremely rugged
design. Many other extension configurations are known (e.g., for
sidewall coring and fluid sampling tools) and may be suitable for
incorporation into a pulsed electric drilling bit.
[0026] FIGS. 5A-5C show a variety of illustrative borehole
configurations having variable cross-sections. FIG. 5A shows a
borehole with a primarily circular cross section, but with a cavity
cut into the sidewall in preparation for a multilateral diverter.
This cavity can be created with a pulsed-electric drilling
electrodes on a semi-cylindrical extension hinged at its top edge
to the bottomhole assembly. As the extension is pressed outwardly
from the bottomhole assembly, the electric arcs pulverize the
material and permit it to be flushed from the cavity. The extension
can then be returned to a flush position in the bottomhole
assembly, leaving a pre-cut cavity that makes it easy to land a
deployable diverter without requiring a large excavation around the
perimeter of the borehole, as is commonly done today.
[0027] FIG. 5B shows an illustrative borehole with a square
cross-section and a square side cavity, which may be useful for a
side-pocket type of Smart Well instrument, or may be used for
position indexing. The drill string may be configured to cut such a
cavity at a precise distance from, e.g., the bottom of the
borehole, a formation boundary, or an anchored assembly. The cavity
can then be detected by subsequently lowered instruments or even
used as a secure landing for anchoring such instruments.
[0028] FIG. 5C shows a nominally circular borehole with a series of
teeth along opposite sides of the borehole. The drill bit can cut
such teeth by periodically deploying a set of electrodes to cut the
teeth to the desired shape. Such teeth may prove useful for
securely anchoring a concrete plug or providing enhanced traction
to a tractor device that pushes the bit.
[0029] FIGS. 5D-5G show a variety of illustrative transverse
cross-sections for a borehole. These cross-sections may be suitable
for use in boreholes having a cross-section that is constant or
variable along the length of the borehole. FIG. 5D shows an
illustrative borehole with a cross-section in the shape of a square
having a fin extending from each corner thereby creating the shape
of a cross. The fins may prove useful for increasing borehole
surface area or maintaining alignment of a steering assembly where
very precise steering is desired.
[0030] FIG. 5E shows a triangular borehole cross section.
Triangles, squares, and other regular polygons offer reduced
contact between the drillstring and the borehole wall with a
tradeoff between the number and depth of the corners in the
cross-section. The contact (and drag) on the drillstring can be
made fairly independent of drillstring position if the
cross-section turns along the length of the borehole to form a
helix much like the threads on a bolt. For example, the bit could
be turned 1-3.degree. for each inch of forward progress to provide
a thread pitch in the range of one turn every 10-30 feet. Shallower
pitches are also envisioned, up to one turn every 0.5 foot, which
translates into a turn of 60.degree. for every inch of forward
progress. Intermediate turning rates (e.g., 5-10.degree./in,
12-15.degree./in, 18-24.degree./in, and 30-45.degree./in) may also
be acceptable. Such rotation is also applicable to the other
cross-sectional shapes and may assist with hole cleaning (i.e., the
flushing of debris from the borehole). The wall contact may be
further reduced by making the drillstring-contacting portions of
the wall convex, as shown in FIG. 5G.
[0031] Unprecedented shaping and steering precision may be
achievable with the disclosed systems. As previously mentioned,
fins or grooves can be cut into the borehole wall and used to
minimize rotation and vibration of the bit. In addition, the
bottomhole assembly that has been stabilized in this manner can
achieve a more precise deviation angle and direction during a
geosteering process. The electrodes need not be limited to the bit,
but may be spaced in sets along the bottomhole assembly to refine
and improve the shape of the borehole to, e.g., to ensure the
wellbore is perfectly round or any other desirable shape, and
smoothly follows a true centerline without any spiraling or
ledging. Moreover, the disclosed systems can be used for
"pre-distorting" a borehole in a stressed formation. If the
borehole is cut in an elliptical cross-section (see, e.g., FIG.
5F), with the ellipse sized and oriented correctly, the formation
will return the borehole to a circular cross-section as the
formation relaxes. Consequently, it becomes possible to achieve a
borehole with an extremely precise circular (or noncircular) shape
and consistently straight over long intervals.
[0032] FIG. 6 is a function-block diagram of illustrative drilling
system electronics. A pulsed-electric drill bit 602 is driven by a
system control center 604 that provides the switching to generate
and direct the pulses between electrodes, monitors the electrode
temperatures and performance, and otherwise manages the bit
operations associated with the drilling process (e.g., creating the
desired transient signature of the spark source, modifying the
position of movable electrode extensions). System control center
604 is comprised of either a CPU unit or analog electronics
designed to carry out these low level operations under control of a
data processing unit 606. The data processing unit 606 executes
firmware stored in memory 612 to coordinate the operations of the
other tool components in response to commands received from the
surface systems 610 via the telemetry unit 608, including e.g.,
reconfiguring the shape of the bit, cutting a core for retrieval,
etc.
[0033] In addition to receiving commands from the surface systems
610, the data processing unit 606 transmits telemetry information
including collected sensor measurements and the measured
performance of the drilling system. It is expected that the
telemetry unit 608 will communicate with the surface systems via a
wireline, optical fiber, or wired drillpipe, but other telemetry
methods can also be employed. A data acquisition unit 614 acquires
and stores digitized measurements from each of the sensors in a
buffer in memory 612.
[0034] Data processing unit 606 may perform digital filtering
and/or compression before transmitting the measurements to the
surface systems 610 via telemetry unit 608. In some embodiments,
the data processing unit performs a downhole analysis of the
measurements to detect a condition and automatically initiates an
action in response to detecting the condition. For example, the
data processing unit 606 may be configured to detect a change in
rock morphology and may automatically cause sample acquisition unit
616 to cut a core sample for transport to the surface. As another
example, the data processing unit 606 may be configured to detect a
formation bed boundary and may automatically steer a course
parallel or perpendicular to that boundary. In such embodiments,
the bottomhole assembly may include a steering mechanism that
enables the drilling to progress along a controllable path. The
steering mechanism may be integrated into the system control unit
604 and hence operated under control of data processing unit
606.
[0035] FIG. 7 is a flowchart of an illustrative drilling method.
The method begins in block 702 with the system extending a borehole
into a formation using a pulsed-electric drill bit. Generally, this
operation occurs when the drill bit is maintained in position at
the bottom of a borehole to drive pulses of electrical current into
the formation ahead of the bit, thereby detaching material from the
formation and extending the borehole. A flow of drilling fluid
flushes the detached material from the borehole. In many method
embodiments, the bit is not rotated. In other contemplated
embodiments, the bit is rotated slowly to create a helix pattern
along the length of the borehole.
[0036] In block 704, the bottomhole assembly collects
logging-while-drilling (LWD) data. Such data may include properties
of the formation being penetrated by the borehole (resistivity,
density, porosity, etc), environmental properties (pressure,
temperature), and measurements regarding the performance of the
system (orientation, weight on bit, rate of penetration, etc). In
block 706, the system processes the data to determine whether the
bit should be reconfigured. Blocks 702-706 are repeated until the
system determines that, due to some condition, the operation of the
bit should be modified. When the system determines that this is the
case, the system adjusts the bit configuration in block 708.
Illustrative examples include extending or retracting arms 72 (FIG.
4), performing operations to vary the cross-section of the borehole
(FIGS. 5A-5C), cutting a core, or angling the bit for
geosteering.
[0037] Numerous variations and modifications will become apparent
to those skilled in the art once the above disclosure is fully
appreciated. For example, the bit can be mounted on a sleeve or a
swivel that enables the drillstring to rotate up to hundreds of
rotations per minute (RPM) while the bit simply slides without
rotation. It is intended that the following claims be interpreted
to embrace all such variations and modifications where
applicable.
* * * * *